SONET is a standard for optical transport formulated by the Exchange Carriers Standards Association (ECSA) for the American National Standards Institute (ANSI), which sets industry standards in the U.S. for telecommunications and other industries. The standard has also been incorporated into the Synchronous Digital Hierarchy recommendations of the Consultative Committee on International Telegraph and Telephone (CCITT) (now called the International Telecommunications Union [ITU]), which sets standards for international telecommunications. Synchronous Optical Network (SONET) and Synchronous Digital hierarchy (SDH) (hereinafter referred to as “SONET/SDH) are now mature digital transport technologies, established in virtually every country in the world. When SONET/SDH was first conceived in the early 1980s, telecommunications traffic was predominantly voice. During the last years there has been a burst in the demand for bandwidth driven mainly by Internet access, e-commerce and mobile telephony. This increase in demand has, so far, been primarily satisfied through a combination of time division multiplexing (TDM), which enables transmission of multiple signals simultaneously over a single transmission path, and dense wave division multiplexing (DWDM), wherein multiple wavelengths are transmitted through a single fiber. However, as the network evolves to higher line rates, the physical limitations of the transport medium (optical fiber) become critical. Furthermore, there remains an overriding requirement to control the cost of providing and improving the level of service to the users.
Optical transport network (OTN) was conceived in 2001, under the auspices of the International Telecommunication Union (ITU) (http://www.itu.int/ITU-T/), to overcome the drawbacks of SONET/SDH. The OTN capabilities and facilities are published as a new standard, known as ITU-G.709 “Network node interface for the optical transport network (OTN)”, which is fully incorporated herein by reference, as if fully set forth herein. The OTN standard is based on the G.975 standard, however, some key elements have been added to improve performance and reduce cost. These include management of optical channels in the optical domain, forward error correction (FEC), to improve error performance and enable longer optical spans, and a standardized method for managing optical wavelengths (channels) end to end without the need for processing of the payload signal.
Reference is now made to FIG. 1A where an illustration of a typical SONET/SDH frame is shown. A SONET frame as defined, for example in the ANSI T1.105, and G.707 for SDH standards, may be thought of as a two-dimensional array of bytes, or a data block, having a length and a width. The length and width are referred to as rows and columns. Each frame includes nine rows and ninety columns (9×90). The first three columns are used for overhead management of the SONET/SDH frame. The other columns provide a synchronous payload envelope (SPE). SPE carries the information that must traverse the entry and exit points through the SONET/SDH network. This information includes both the payload traffic and the path overhead. The path overhead coordinates the activities between the SONET terminals (or add/drop multiplexors) that are responsible for the entry and exit points through the network. The SONET frame is a synchronized frame, the beginning of which may be indicated by a frame signal. This frame format is used for all SONET/SDH transmissions. As the data rates increase, more copies of the frames are transmitted for each transmission period. Typically, SONET/SDH frames are wrapped with a digital wrapper used for error detection and correction. Error correction is performed, as defined in the G.975 standard, with a wide range of applications in digital communications, by means of the well known in the art Reed-Solomon algorithm (see http://www.itu.int/ITU-T/). SONET/SDH protocols are capable of handling two different types of flows: a) time division multiplexing (TDM); and, b) flows that contain data packets, such as IP, ATM, GFP, 1GBE and 10GBE. TDM is typically used for telecom applications. The frame shown in FIG. 1A typically refers to STS-1, which is the basic frame for the SONET, or to STM-0, which is the equivalent of SDH.
Reference is now made to FIG. 1B where an illustration of an OTN frame is shown. An OTN frame consists of three distinct parts, two of which that are broadly similar to the SONET/SDH frame, namely an overhead area and a payload area. In addition, the OTN frame includes a forward error control (FEC) area. The FEC scheme used in the OTN is a Reed-Solomon RS (255,239) code. This means that for every 239 bytes of data, an additional 16 bytes of data (code words) are added for the purpose of error correction. These additional bytes, when used for error correction in data flows, can enable correction of 8 symbol errors in the FEC code word (FEC section in the OTN frame). When used for error detection, these additional bytes can enable detection of 16 symbol errors. The size of the OTN frame is four rows of 4080 bytes. Data is transmitted serially beginning at the top left, first row followed by the second row and so on and so forth. There are three line rates currently defined in OTN: 1) 2.5 Gbit/s—optical channel transport unit 1 (OTU1); 2) 10 Gbit/s—optical channel transport unit 2 (OTU2); and, 3) 40 Gbit/s—optical channel transport unit 3 (OTU3). The actual rates of OTU1, OTU2 and OTU3 are 2.66 Gbps, 10.7 Gbps and 43 Gbps respectively. From this point we will refer to the basic rates (i.e. 2.5 Gbps, 10 Gbps and 40 Gbps).
The overhead area includes two sections shown in FIG. 1C. The overhead sections include the optical transport unit (OTU) together with the optical data unit (ODU), i.e., OTU/ODU, and the optical payload unit (OPU). The OTU overhead, located in row 1 columns 8–14, provides supervisory functions such as section monitoring (SM), and general communication channel (GCCO). The ODU overhead is placed in columns 1–14 of rows 2, 3 and 4 of the OTN frame. The ODU information structure provides tandem connection monitoring (TCM), end-to-end path supervision, and client signal adaptation via the optical channel payload unit (OPU). The OPU overhead is added to the OPU payload and contains information to support the adaptation of client signals. The OPU overhead is located in rows 1–4 of columns 15 and 16 and is terminated where the OPU is assembled and disassembled. The frame alignment signal is located at row 1 columns 1–6. A detailed description of the OTN frame is provided in “ITU-T G.709 Interface for optical transport network (OTN)” (http://www.itu.int/ITU-T/), which is fully incorporated herein by reference, as if fully set forth herein.
Reference is now made to FIG. 2 where an exemplary network 200, that includes OTN sub-network with standard interface IrDI and OTN sub-network with proprietary interface IaDI. Network 200 includes inter-domain interfaces (IrDIs) 210, and intradomain interfaces (IaDIs) 220. IrDIs 210 are the boundaries between OTNs of different administrative domains. The administrative domains may be that of multiple network operators and/or equipment vendors. IrDIs 210 may be used as interfaces between different networks or between different IaDIs 220 within the same network operator. IaDIs 220 may be any interface within a single vendor sub-network, which may or may not extend to include the entire carriers. IaDIs 220 are not part of the OTN standardization except for properties necessary for network management. Hence, IaDIs may not necessarily be compliant with the OTN standard. This non-compliance may result in significant limitations when incorporating Intra-corporate networks (which are SONET based optic networks) into Optical data networks that are OTN based. Currently such hybrid networks therefore require significant investment in complex interface design in order to run such a network effectively. Network 200 is an example of such a network.
Due to the complexity of the interfaces described hereinabove, there is a widely recognized need for, and it would be highly advantageous to have, a solution that provides an efficient data flow in networks comprised of a variety of sub-networks and interfaces, including both inter and intra domain interfaces, that are compliant with different standards, for example, networks that combine SONET/SDH and OTN standards.